This invention relates in general to silicon on diamond circuits, and in particular, to a method for separating dies of silicon on diamond.
Diamond has valuable thermal and electrical properties which are highly desirable in microelectronic circuits. Diamond has the highest thermal conductivity of any known material. At room temperature, diamond is about five times as thermally conductive as copper. Diamond is also an excellent electrical insulator and has a superior dielectric strength. As such, diamond makes an excellent material for heat sinks in microelectronic circuits. The ability of diamond to insulate the circuit and rapidly remove heat from the circuit increases the overall performance of microelectronic circuits because their speed deteriorates with heat. Moreover, heat also contributes to the early failure of microelectronic circuits.
Until recently diamond has not been a useful material due to the difficulty of integrating it into existing circuit fabrication techniques. However, recent advances have enabled those skilled in the art to deposit layers of diamond using chemical vapor deposition techniques. One such technique is described in "Chemical Vapor Deposition of Diamond for Electronic Packaging Applications," David J. Pickerel and David S. Hoover, Proceedings, First International High Temperature Electronics Conference, Jun. 16-20, 1991.
Another well-known property of diamond is its hardness. This property renders it difficult to separate the dies of wafers having diamond layers. In a typical die separation process, a circular saw having a diamond-coated blade is used to remove silicon from the area between dies. This operation is normally carried out on a wafer dicing machine. The wafer is affixed to an adhesive surface of a film material that is mounted on a frame. The frame and wafer are placed beneath the saw and the saw cuts through the wafer and partially into the membrane of the film. Thereafter, the die are removed from the film with a pick and place machine that mounts the die into a chip carrier or other package.
However, such traditional methods of die separation are unsatisfactory for wafers with diamond layers. Due to the hardness of diamond, circular diamond saw blades are rapidly worn out. Thus, those skilled in the art have resorted to a scribe and break method for separating die. Using that method, a saw partially penetrates the diamond layer. Thereafter, the die are separated along the scribe marks in the diamond layer by mechanically snapping the layer over a surface disposed beneath the partial scribe line. This method is akin to the method used to cut glass with a scriber. The problem with such method is that it often applies mechanical stresses across the wafer so that the risk of damage to the electronic circuits on the die is high.
In view of the above problems, it would be desirable to have a reliable method for separating silicon on diamond dies.